The present invention concerns a partial disc prosthesis.
Disc prostheses, which can be partial or total, are normally intended to replace all or part of an intervertebral disc when the latter has been destroyed by surgery or by disease.
A first type of disc prosthesis consists of a rigid cage which, for example, can be rectangular in cross section, and in which perforations are formed for receiving grafts which are intended to ensure satisfactory attachment of this cage with the two vertebrae between which it is to be inserted. This type of rigid cage, which is implanted in particular by impaction or screwing, has a disadvantage in that it leads to complete blocking of the two vertebrae between which the cage is arranged, and this limits the patient""s freedom of movement.
An intervertebral disc prosthesis is also known from the document EP-A-0,346,269, which prosthesis is made up of a core of viscoelastic material interposed between two metal cover plates which, after they have been implanted, are intended to be in contact with the surface of the vertebrae. However, this type of prosthesis has a disadvantage which lies in particular in its lack of stability, so that there is a considerable risk of this prosthesis being ejected from the intervertebral space.
In order to overcome the abovementioned disadvantages of the prior art, the invention proposes a partial disc prosthesis which can be anterior or posterior, can be implanted easily in the intervertebral space, possesses satisfactory stability within this intervertebral space, and permits sufficient freedom of movement while at the same time guaranteeing a physiologically advantageous posture.
To this end, the invention relates to a partial disc prosthesis intended to be inserted between two adjacent vertebrae, of the type comprising a core made of an elastic material such as a silicone polymer or an elastomer, covered, over part of its periphery, by a casing made of a rigid material and intended to be in contact with the said two adjacent vertebrae, characterized in that the said core comprises, in cross section, two end portions connected by a middle portion, the said casing comprises two covers provided with a threading and covering, at least partially, the external periphery of the said end portions, and the distance separating the said covers increases towards the anterior part of the prosthesis.
The invention also proposes an implantation instrument for the prosthesis as described above, which instrument ensures easy implantation of the prosthesis, can be easily withdrawn once the prosthesis has been implanted, and makes it possible to preserve the integrity of the various organs around which this instrument is manoeuvred during all these operations.
To this end, the invention also relates to an implantation instrument for the prosthesis as described above, characterized in that it comprises a grip handle which is continued via means for securing the said prosthesis relative to the said instrument, in a transversely compressed state of the said prosthesis.